This invention relates to separation membranes and to methods for removing water from organic compounds using separation membranes.
The effective removal of water from organic fluids is important in pollution control and in numerous industries such as in distilleries, the preparation of the anhydrous chemicals and the like. While gross separations are comparatively simple when the organic compound is immiscible with water, many organic compounds are partially or completely soluble in water. Separation of such organic compounds from water is sometimes carried out by distilling the mixture but this process requires large amounts of energy. Moreover, some organic liquids which have boiling points close to that of water or which form azeotropic mixtures with water cannot be readily separated using a distillation process.
It has been found that certain materials, when formed into thin membranes, possess the capacity to selectively permit water to pass therethrough while preventing the passage of organic compounds. Thus, Binning et al. in U.S. Pat. Nos. 2,953,502 and 3,035,060 teach the separation of ethanol from water using cellulose acetate and hydrolyzed polyvinyl acetate membranes. Chiang et al. in U.S. Pat. Nos. 3,750,735; 3,950,247; 4,035,291 and 4,067,805 describe the separation of formaldehyde from water employing a variety of membranes.
Unfortunately, previously known separation membranes do not exhibit a selectivity as high as desired for many applications; that is, the water which permeates therethrough contains substantial amounts of organic compounds. Thus, it would be desirable to develop a separation membrane which more efficiently separates water from organic compounds.